Robot capabilities range from very simple repetitive point to point motions to extremely versatile movement that can be controlled in sequence by a computer as a part of a complete integrated manufacturing system. Robots have been used in many material processing applications including cutting, trimming and welding.
Laser applications can be divided into several general categories including the measurement of spacial parameters, material heating and/or removal, non-destructive probing of resonant phenomena, communications, optical processing, laser-induced chemical reactions and weapons.
The combination of a laser with a robot allows the laser to operate with a degree of freedom previously unknown. The combination of the two technologies, if successfully performed, is suitable for most laser applications, including material processing applications. The same laser can be used in processing many kinds of materials by controlling the speed and the power of the laser. This laser can cut metal, cut glass, trim plastic or weld aluminum. Because robots are typically controlled by a programmed computer, the same computer can be used to regulate the laser's power. Consequently, in a flexible manufacturing line, parts can be cut or welded one after the other simply by adjusting the power of the laser.
Lasers are currently in operation in both commercial and industrial environments. For example, many parts of an automobile are processed with lasers. Also, a large percentage of vision systems that measure depth are laser-based.
Another industrial use of the laser is laser-assisted machining wherein the laser beam is applied in front of a cutting tool to reduce tool wear and cutting forces. Such an application results in fewer tool changes, decreased total tool wear and tool cost, increased cutting speeds and increased amounts of materials that can be cut.
Two types of lasers are typically used in material processing applications, solid state and carbon dioxide lasers. The carbon dioxide lasers are relatively unlimited in power. The solid state lasers are limited in power and require more elaborate shielding than the carbon dioxide lasers.
Popular uses for metal-working lasers include seam, spot and fusion welding, cutting, drilling, surface hardening, metal marking, scarfing, deburring, trimming and heat treating. The advantages of laser processing are particularly evident in welding. Welding done with lasers often requires no additional work such as grinding. With traditional welding, welds must be reworked a large percentage of the time. Therefore cost savings are an important aspect of laser welding.
Two methods have developed in order to link lasers with robots. One method is to move a part via a robot into the laser beam. The other way is to move the beam via the robot to the part. The latter method is effective if the part is too large to be moved easily or when contouring is necessary.
One relatively new concept of linking robots with lasers is using more than one robot to share a laser beam. Sharing systems are only limited by the cycle times of the various operations being done.
Another concept that is relatively new is mounting the laser on the top of an articulated-arm robot.
Another method of linking the robot with a laser incorporates two mirrors in each joint of a laser arm which is manipulated by the robot. The mirrors must be held in place very securely and precisely for the beam cannot be misdirected a fraction of a degree as it proceeds along its path. Vibrations of the robot that could affect the mirror positions must be taken into account in such a design. A focusing lens concentrates the laser energy and directs it to a singular point with a high power density. The robot must be very accurate to direct the beam to a precise area on a workpiece. A longer focal length lens can be used to compensate for robot inaccuracies. However, the resulting beam is focused over a larger area so that both power density and speed are lower.
Despite the above-noted problems in linking the laser with the robot, it is highly desirable to forge this linkage especially because the laser is an ever sharp tool having a non-contact method of operation. The use of the laser also eliminates the need for tactile feedback, adaptive circuitry, sensory perception and tool wear because the laser and the part do not touch each other.
As previously mentioned, in manipulating high power laser beams in welding robots, the beam is usually reflected off several mirrors located at the joints of a tubular linkage mechanism which has several articulations. The mechanism is then manipulated by the robot to direct the laser focal point along the desired path. Two mirrors are usually required at each joint to direct the beam from one link orientation to another. Since manipulators generally require five to seven articulations to provide the necessary motion to access the workpiece at a specific orientation the number of mirrors needed to provide the laser beam at the workpiece can be as many as 14. Accuracy of the laser path depends on the accuracy of the robot and laser arm and mirror alignment which are not corrected for by programming. Also, power loss, overheating and cracking, misalignment, higher cost of accuracy and space and weight limitations make this approach impractical for general purpose manipulators. Such an approach is disclosed in the U.S. Pat. No. 3,913,582 to Sharon.
U.S. patents which disclose rotatably adjustable mirrors include the U.S. Pat. Nos. 3,528,424 to Ayres, Ditto 4,059,876 and Malyshev et al 4,144,888.
The U.S. Pat. No. 4,429,211 to Carstens et al., discloses a pipe welding system including a seam tracker to keep the focal spot on the seam to compensate for axial and radial variations of the pipe. An active beam alignment system operates in real time to compensate for angular misalignment. Individually controlled mirrors reflect the laser beam in order to weld the pipe.
Other patents of less relevance include the U.S. Pat. Nos. 3,736,402 to Mefferd et al., Fletcher et al 3,888,362 and Sakuragi et al 4,443,684.